1. Field of the Invention
The present invention is broadly concerned with glass/nanoparticle composites, and especially composites containing embedded nanocrystals having desirable electrooptical properties allowing the composites to be used in high density recording media. More particularly, the invention is concerned with such composites, and methods of fabrication thereof, wherein the composites include a glass matrix body with rare earth iron garnet nanoparticles embedded therein. The composites are manufactured by contacting a suitable porous glass with a colloidal dispersion of nanoparticles to fill the glass pores, followed by heating of the treated glass to effect fusing of the glass matrix pores.
2. Description of the Prior Art
Ferromagnetic fine particles such as nanoparticles have attracted considerable attention from researchers in recent years. This interest stems from the fact that such particles are single magnetic domain particles and accordingly their magnetic properties and their mutual interaction can be studied without magnetic domain effects. Moreover, quantum size effects and the magnetic quantum tunneling effects of these particles can be studied because of their nanoparticle dimensions. From an industrial standpoint, such magnetic particles can be used as media for high-density magnetic or magneto-optical information storage.
In light of these considerations, efforts have been made in the past to prepare nanoparticle compositions using a variety of different methods. A consistent problem with these prior techniques has been the tendency of the magnetic nanoparticles to spontaneously coagulate. Thus, the intrinsic magnetic characteristics of the nanoparticles are often difficult or impossible to discern even though the nanoparticle compositions were initially successfully prepared. A number of methods have been proposed to prevent the coagulation of magnetic nanoparticles, such as to disperse the particles in an organic binder (O""Grady et al., J. Magn. Mater., 95:341 (1991)), or to disperse the particles in a solvent with an aid of a surfactant (Rosenweig, Ferrohydrodynamics, Cambridge University Press, 1985). These methods use mechanical stirring to disperse the particles, but nevertheless a considerable portion of the particles remain coagulated if the particle concentration is high.
In other research, magnetic fine particle precursors have been dispersed in sol-state glass precursor, the magnetic particles were precipitated in solidified glass or simple magnetic fine particles (e.g., elemental iron or cobalt or simple crystalline structure such as iron oxide) were introduced into the pores of porous glass. However, owing to the fact that these techniques involve the precipitation of precursor particles into a glass matrix, or ion sputtering on porous glass, it has been difficult to control the fabrication of the products. As a consequence, these methods have not been applicable using fine particles of complex crystalline structure.
The present invention overcomes the problems outlined above and provides new glass/nanoparticle composites and methods of fabrication thereof, allowing controlled production of very high nanoparticle density composites. Broadly speaking, the composites of the invention include a body of glass having embedded therein a plurality of heterologous nanoparticles, with at least certain of the nanoparticles having a diameter of up to about 500 nm. Preferably, the nanoparticles are characterized by the property of altering the polarization of incident electromagnetic radiation which is reflected or scattered from the nanoparticles. The most preferred type of nanoparticles are the rare earth iron garnet nanocrystals, especially yttrium-iron nanoparticles. Here, the term xe2x80x9cnanoparticlexe2x80x9d is defined as a particle, the size of which is between several nanometers and several hundred nanometers. The term xe2x80x9cnanocrystalxe2x80x9d is defined as a crystal grain the size of which is between a several nanometers and several hundred nanometers.
In forming the composites, a porous glass body such as xe2x80x9cthirsty glassxe2x80x9d is contacted with a dispersion including the heterologous nanoparticles, so that such nanoparticles locate within the surface pores of the glass body. Thereafter, the nanoparticle-treated glass body is heated to fuse the pores and embed the nanoparticles. Most preferably, the nanoparticles are initially in an amorphous state, and the heating step serves to transform these nanoparticles into a crystalline state. These methods produce stable composites which can be used as a part of electrooptical recording media. Nanoparticle loadings on the order of 109 nanoparticle/mm2 of glass surface area are possible. This allows construction of recording media having a recordable data density many times greater than conventional media.